Did you set up the throttle range as is required for most electric's when you first started the motors .
Most ESC's will have also have a fail safe in case of throttle being on reverse.
Have posted this before but for your benefit once again:
Procedure for using Brushless Electric Power Systems for RC Models
1) Turn on the transmitter first
2) Raise Throttle to maximum Position
3) Connect Battery to ESC
4) You should get a sound signal confirming setting of Max throttle position
5) After hearing a long beep confirming the max position of throttle reduce throttle to Zero
6) You should hear a sound signal confirming the minimum throttle position followed by a long beep or a set of beeps confirming the minimum throttle position .
7) Thus the throttle range has been set up.
While disconnecting the battery kindly note the Battery has to be disconnected from the ESC before the transmitter is switched off.
IMPORTANT NOTE
If the transmitter is turned off before the battery is disconnected there is a very high possibility of damaging the servos and other radio systems.
Majority of the ESCs currently available in the market today use this procedure for powering on and off .
Lithium Polymer batteries require the use of special LIPO charger and at no time should they be charged with regular available chargers.
IT IS ADVISABLE TO USE THE ABOVE POWERING ON AND OFF PROCEDURE EVRYTIME THOUGH IT IS NOT ESSENTIAL
THIS IS ESSENTIAL AS THE ESC HAS TO UNDERSTAND THE MAX AND MINIMUM THROTTLE POSITION.
If you have any issues let me know .
Sai